In order to establish a molecular basis for comparisons of pathogenicity, oncogenicity and host-cell range of human polyomaviruses, four specific studies of JC virus (JCV) will be conducted. The studies will provide fundamental information about the molecular biology of JCV which has been unattainable in the past. The information will form a foundation for comparing JCV, BK virus, and primate polyomaviruses in future research. Several isolates of JCV have been cultured from diseased brains of patients with progressive multifocal leukoencephalopathy. The DNAs of some isolates are heterogeneous in size and may be defective. The genomes of representative isolates have been cloned as r binant DNA. Therefore JCV and its interaction with host cells can and will be examined in the following ways: (1) For the purpose of identifying strain differences and to provide a detailed physical map, cloned DNAs from several isolates will be mapped with restriction endonucleases. (2) To study genetic variation in JCV further, cloned and natural DNAs having deletions will be mapped by cleavage with restriction endonucleases and by heteroduplex mapping. Infectivities and transforming abilities will be tested. (3) JCV-induced hamster and owl monkey tumor cell lines and JCV-transformed hamster brain cells will be analyzed for integrated viral DNA to determine whether integration and methylation patterns differ between the two species of host cells or among viral isolates. (4) As a step in understanding the host range, JCV DNA synthesis will be studied in permissive and semi-permissive cells and in untested New World primate cells and human cell lines.